Most excitatory neurotransmission in the adult central nervous system is mediated by glutamate, thus the molecular organization of glutamatergic synapses has received much attention in recent years. Many proteins that interact with glutamate receptor subunits have been isolated by in vitro binding assays [Scannevin and Huganir, 2000], but information on anatomical distribution and function in the intact CNS is lacking. The first goal of the research proposal is to determine the colocalization of GluR2 with PICK1 and GRIP1, both of which have the capability of binding GluR2 [Dong et al., 1997; Xia et al., 1999]. The second goal is to assess whether PICK1 and GRIP1 are expressed in principal neurons or interneurons by determining colocalization with interneuron markers, and the third goal is to determine if the distribution of GRIP1 and PICK1 is regulated by sound stimulation.